Electromagnetic transducer head



sept. 11, 1962 3,053,939

M. CAMRAS ELECTROMAGNETIC TRANSDUCER HEAD 5 Sheets-Sheet 1` Filed Feb. 25, 1954 L7. YE 27 ZL: T"

Marr/J1 amf'a Sept. 11, 1962 M. cAMRAs 3,053,939

ELECTROMAGNETIC TRANSDUCER HEAD Filed Feb. 25, 1954 5 sheets-sheet 2 125.77 IDT Sept 11, 1962 M. CAMRAS 3,053,939

ELECTROMAGNETIC TRANSDUCER HEAD Filed Feb. 25, 1954 5 Sheets-Sheet 3 E7 .z/"E 712A D T Marl/n Camr'as Sept. 11, 1962 M. cAMRAs 3,053,939

ELECTROMAGNETIC TRANSDUCER HEAD Filed Feb. 2s, '1954 5 Sheets-Sheet 4 ongur 50 Dls TANCE (mm.)

50 zo F q- J0 w ou'rPuT40 o (d b) 0 2050i moo '1mm FREQUENCY Marl/22 amras H LiL-77E Sept. 11, 1962 M CAMRAS 3,053,939

ELECTROMAGNETIC TRANSDUCER HEAD Filed Feb. 25, 1954 5 Sheets-Sheet 5 Mam/n Camra United States Patent 3,053,939 ELECTRUMAGNETIC TRANSDUCER HEAD Marvin Camras, Chicago, Ill., assignor to Armour Re- Search Foundation of Illinois institute of Technology,

Chicago, Ill., a corporation o Illinois Filed Feb. 23, 1954, Ser. No. 411,608 13 (Ilmms. (Ci. 179-1002) This invention relates to an electromagnetic transducer device and particularly to such a device for reproducing a signal recorded on a magnetic record medium.

-It is an object of the present invention to provide a novel electromagnetic transducer head.

:It is an additional object of the present invention to provide a transducer head capable of responding to D.C. uX, iniinite wavelengths, or zero speed of a magnetic record medium.

It is a further object of the present invention to provide a transducer head with an e'icient magnetic circuit for maximum sensitivity.

It is another `object of the present invention to provide a transducer assembly that is relatively insensitive to stray fields and is easily shielded.

vIt is still another object of the present invention to provide a compact unitary transducer structure requiring little or no additional amplication to operate a speaker or an indicating instrument.

It is yet another object of the present invention to provide a transducer head of high stability with respect to operating voltages, aging and the like.

It is a still further object of the present invention to provide a transducer head having a non-linear response characteristic such `as a logarithmic response.

It is another and still further object of the present invention to provide a head having both transducing and amplifying properties.

Other and further important objects of this invention will be apparent from the -disclosures in the specification and the accompanying drawings.

On the drawings:

FIGURE l is a somewhat diagrammatic longitudinal sectional view of an electromagnetic transducer head according to the present invention;

FIGURE 2 is a somewhat diagrammatic longitudinal sectional view of the structure of FIGURE 1 but taken in a plane at right angles thereto;

FIGURE 3 is a transverse sectional view taken substantially along the line III- III of FIG. 1;

FIGURE 4 is a diagrammatic transverse sectional view of the transducer head of FIG. 1, but illustrating diagrammatically a modied pole piece configuration for providing a logarithmic characteristic response;

FIGURE 5 is an end elevational View of the structure of FIG. 2;

FIGURE 6 is a diagrammatic side elevational view of a modied pole piece configuration for improving the eiciency of beam deection;

FIGURE 7 is a diagrammatic side elevational view indicating the stream of electrons between the target anodes in the absence of an applied magnetic field;

FIGURE 8 is a diagrammatic view similar to FIG. 7, but illustrating the beam under the inlluence of a high play-back magnetic iield;

FIGURE 9 is a diagrammatic View similar to FIG. 7, but illustrating the situation with converging target anodes;

FIGURE 10 is a diagrammatic view similar to FIG. 7 and illustrating the case of a divergent stream of electrons between the target anodes;

FIGURE 11 illustrates a push-pull type circuit suitable for sensing the eilect of a magnetic signal on the stream of electrons between the target anodes;

3,653,939 Patented Sept. 11, 1962 ICC FIGURE 12 illustrates a single-ended circuit for sensing the eiiect of the signal flux on the stream of electrons;

FIGURE 13 illustrates a circuit for the transduceramplifier head of the present invention;

FIGURE 14 illustrates a high frequency equalizer circuit connected `between the transducer head and the first ampliiier stage in accordance with the present invention;

FIGURE 15 is a somewhat diagrammatic longitudinal sectional view illustrating a first form of a short type electronic transducer head according to the present invention;

FIGURE 16 is a diagrammatic end elevational view of the head of FIGURE 15;

FIGURE 17 is a diagrammatic side elevational view of washer type pole pieces suitable for use with the head of FIGURE 15;

FIGURE 18 is a diagrammatic front elevational view of a modified form of pole structure and indicating the manner in which recording windings may be applied t0 the pole pieces, the pole pieces being adapted Ifor playback from a wide channel tape record member;

FIGURE 19 is a diagrammatic top plan view of the structure of FIGURE 18;

FIGURE 20 is a diagrammatic side elevational view of the structure of FIGURE 18;

FIGURE 21 is a diagrammatic front elevational View of a third form of pole piece structure utilizing overlapping pole pieces;

FIGURE 22 is a diagrammatic plan view of the structure of FIGURE 21;

FIGURE 23 is a diagrammatic side elevational view of the structure of FIGURE 21;

FIGURE 24 is a diagrammatic vertical sectional View illustrating a half of a pole mounting structure constructed by resin embedding and adapted for mounting the poles of FIGS. 18-20;

FIGURE 25 is a transverse sectional view of the structure of FIGURE 24;

FIGURE 26 is a diagrammatic longitudinal `sectional view illustrating a short type electron-cloud transducer head provided with a shield or baille element for protecting the anodes from stray beam currents;

FIGURE 27 is a diagrammatic illustration of a circuit for use with an electronic transducer head similar to that of FIGURE l, but having the pole pieces of FIGURE 17;

FIGURE 28 is a plot of output as a function of input for the head of FIGURE 27 and indicating the wide range of linearity of the head construction;

FIGURE 29 is a plot of relative ou-tput as a function of the position of the pole pieces along the capillary throat of the tube of FIGURE 27;

FIGURE 30 is a frequency response curve for the head of FIGURE 27;

FIGURE 31 is a diagrammatic longitudinal sectional view of -a flat face type electron-cloud transducer head according to the present invention;

FIGURE 32 is a diagrammatic cross sectional View taken substantially along the line XXXII-XXXII of FIG. 31;

FIGURE 33 is `a diagrammatic view of the pole pieces utilized in the embodiment of FIGURE 3l;

FIGURE 34 is a diagrammatic cross sectional view similar to FIGURE 32, but illustrating the use of half round anodes instead ofthe rectangular anodes shown in FIGURE 32;

FIGURE 35 is a diagrammatic longitudinal sectional view of a further type of electron-cloud transducer head having a `constricted portion for receiving the pole piece construction;

FIGURE 36 illustrates a still further modified form of transducer head construction;

l"FIGURE@Tis/'a diagrammatic illustration of a microphone design using an' electron-cloud tube as `the transducing element;

FIGURE 38 is a diagrammatic end elevational view of the structure` of FIGURE 37;

FIGURE '39'is a diagrammatic illustration of a device 'employing `an electron-cloud tube as the transducing element and suitable as a phonograph pick-up, vibration pick-up, or the like;

FIGURE '40 is a diagrammatic horizontal sectional view of a reflection type electron-cloud transducer head according to the present invention;

'FIGURE 4l is a diagrammatic vertical lsectionalview `off thestructure of FIGURE 4() and illustrating the manner in which the magnetic field is applied to the reflected stream of electrons;

FIGURE 42 is a diagrammatic horizontal sectional *vieWsimilar--to FIGURE 40 but illustrating a modiied rformel? v'polep-iece 'constructionand illustrating the reected stream `of electrons as being deflected toward one ofthe-'anodesg :FIGURE 43 is a diagrammatic end elevational view @illustrating the cooperation of the pole piece structure of -FIGURE 42 with the capillary portion of the tube; and

FIGURE V44 Ais a diagrammatic horizontal sectional `vievvof a further form of reflected type transducer-head wherein the reflected stream of electrons is 'produced `by.' secondary emission.

As shown on the drawings:

A magnetic' transducer device according to the present Iinventionhas Vbeen illustrated in FIGURES land 2 as comprising an evacuated envelopel having an electron gunwstructure 11 for'establishing a stream of electrons in -a restricted capillary section 112 of the tube. By "Way lof example, the electron gun 'structure may include a filament 14, cathode 1S,`iirst grid and heat shie1d'16, 'accelerating-grids 18 Vand focusing grid 19.

A pair of target electrodes 21 and 22 preferably extend falong theilength fof the capillary section 12 of the tube on opposite sides thereof and serve as target anodes for the electron beam. The closed end of the tube23 may have a phosphor indicating coating 24 thereon and an aperture 25, FIGURE .2, for' observing the beam `and thus Vfacilitating adjustments thereof. Theelectrodes 21=and 22 Vmay comprise non-magnetic hollow semi-cylinders generally in the form of troughs. Suitable materials for -the velectrodes are copper, tantaluin, molybdenum and .the like. The troughs 21 and 22,V may be coated with carbon'black toreduce secondary emission. Y Y

Fordefining a `magnetic iield transverse to the stream ofvelectrons'flowing 'between the electrodes 2i and '22, a core 30 is provided Which has a'pair'ofpole pieces 311 'land 32' extending on the exterior of the capillary section i12-ofthe envelopeand generally o-nopposite sides of the electrodes 21 and 22. For applying a signal flux tothe pole piece-s 31 and-32,' the `core may beprovided with a non-magnetic gap 33 adapted to receive a magnetized record-member34 thereacross moving in the direction of the varrow 35. The reluctance of the gap`33 is selected to be of the order of 'magnitudeof the reluctanceof the fga'p between'the prole pieces 31 and 132, FIGURE 2. "For'example, the" capillary. portion of the tubelmay have `an outside diameter of 2 millimeters or mils .-(l 'mil-:0.001 Yinch). -heflen-gth of the capillary section may be approximately 1500-l mils, vWhile the gap 33 ymay be 0.5 mil. On this basis, the reluctance of the'gap 'maybe 0;()0l25, While the reluctance of the path between ,the-pole pieces v31 and 32 in comparable unitsvmaybe 0.000667. The pole pieces may be of a Mumetal from'S tol mils -thick,`or may comprise laminations made from thinnergst'ock or a suitablev ferrite core may housed, dependingv on the upper frequency responsedesired.

As indicated in FIGURE 3, the poles 3l and 32 may fbe shaped `to give a morejuniform `field 'by ,turning the longitudinal edges of the polesrinwardly slightly tofcounteract for the fall of the flux at the edges due to fringing. The configuration ofthe polesA can-'be varied in accord with the response characteristics desired. For example, Ia logarithmic characteristic response is obtained by a shape of the poles such as indicated in FIGURE 4 at 31' and 32. The pole pieces can also be shaped in the longitudinal direction, for example as indicated in'FIG- URE 6 at `31" to give best efficiency of beam deilection.

/For isolating the `tube 10 from external fields, a shield of magnetic material 40 may be provided. The enlarged portion 42 of the tube extends in close fitting relation to Y one end of the shield, and the shield has an aperture 43 thro-ugh which the end of the core 30'having the'gap 33 projects for'contact with `the record member 34. The pole pieces Gland '32 lare preferablyk separated from the Aenvelope 10 and independently supported and damped to prevent microphonics, damping material 45 being provided'for this purpose along with the non-magneticpole 'piccesupport filler 46. The electron tube envelope 10 `may be separated from thepoles and shield for replacegenerally evenly distributed between the two electrodes;

however, -as indicated in FIGURE 8, with the application of a iieldfrom the magneticpole pieces, the cloud of electrons has a net drift to one or the other of the'anodes, here to anode 21. Sensitivity is -greater When a 'lower voltagefis applied to the `anodes than to the accelerating grids 18. In this case,'a deceleratingaction is'provided creating slower moving electrons in the region of deecltion.

As illustrated Vin FIGURE-9 at 21', 22 the anodes vcan be converging Within limits, without seriously affecting the operation; similarly, the anodes can also be diverging. The reference numeral 49 indicatesbale plates for controllingthenonLdeiiected position of lthe beam in' the regionbetween converging electrodes 21222'.

Alternatively, as illustratedin*FIGUREV l0, a SourceS() Vof a divergent` beam of electrons indicated ati 51, may be utilized Withthe electrodes 21 and 22. It can be 'shown that the change caused by a deflectionof a divergent beam is independent of the angle'of divergence.. giving excellent stability. The diverging beam gives Vstability at the expense of sensitivity, but sensitivity is more ythan ample With this type head in most applications. It can alsobe shown that the-angle of the electrodes,`withinlimits, will not change the sensitivity as long as the electrodes intercept the'beam, andthe beam does not deflect on or ff completely during operation. The Vsensitivity of the illustrated device is, therefore, very stable. `Some factors controlling sensitivity are the sharpness of the cone of the beam, the amount of beam current, accelerating 'voltage in the deilection region (before deiection), and the degree ofconcentration of the'feld in the Vmost effective-region for deflection.

In FIGURE ll is illustratedapush-pull circuit for receiving'the output from'the electrodes 21 Vand'22. In this case, the` variouslgridvoitages are taken from a voltage divideri with the anode voltages'appled to the electrodes 21 -and22 through resistors 61 and 62, so as to' be less than vthe accelerating voltage ongrids 18. The output from the electrodes 21 and 22 is fed into the push-pull 'circuit 63 and the resultant output is taken from theA secondary of transformer 64. In some cases because of secondary emission effects it may be desirable to operate electrodes 21 and 22 above the potential of 18. This is readily accomplished by feeding 61 and 62 from a separate source of higher B+y than the supply used Vfor 18.

In FIGURE l2, is illustrated a single ended circuit wherein the unused target electrode 21 is kept at 20 or more volts negative with respect to the target electrode 22 for reduction of secondary emission effects. This is accomplished by means of the potential divider 70y in cooperation with the movable contacts 71 and 72 connecting with the two electrodes 21 and 22. The output from anode 22 is applied to the single ended amplifier circuit 74. The circuit may be balanced by initially directing the beam so as to favor electrode 21, for example by tilting the gun, or by auxiliary electrodes, or by magnetic deflection, or by bending or curving the capillary.

FIGURE -13 illustrates a circuit including a stage of amplification built into the head tube 80, which is otherwise similar to the tube 10. Here, the high voltage from B+ is supplied through the resistor 100 to the target electrode 22 and Variations in the iiow of electrons to the electrode 22 is transmitted through the condenser 101 to the grid 102 of the amplifying stage within the tube. The electrode 21 is connected directly to B-fthrough the conductor 103. 'Ihe cathode 104 supplies electrons both for the capillary end of the tube and for the amplifying stage including the grid 102 and plate 108 which is supplied with voltage from the B-lsupply through a resistor 109. rIhe output is taken through a condenser 110. The accelerating and focusing voltages are taken ofi the voltage divider 111, similarly to the previous circuits. As previously described the supply voltage to resistor 100 may be from a higher B+ than the other electrodes, so as to operate anode 22 at an equal or higher voltage than anode 21.

FIGURE 14 indicates a high frequency equalizer circuit in the input stage from the electrode 22, the B-lsupply being furnished through a resistor 120 and the output being taken through a single ended circuit similar to that of FIGURE 12, but including a resistor 121 having a condenser y122 in parallel therewith and fed into a resistor 123 for boosting the high frequency output from the tube. It is desirable to have the high frequency equalization before electronic amplification to improve the signal to noise ratio at high frequencies. The fall-off at high frequencies is caused by gap effects, reduced capability of the tape to retain high frequencies, and the like. The head of the present invention is directly responsive to flux, rather than to the rate of change of fiux, as in induction type pick-up devices.

In FIGURES l5, 16 and 17 a short type electron-cloud transducer head is illustrated. The head is generally of the size of a postage stamp and comprises an enlarged cylindrical envelope portion 135 and a flattened capillary portion 136 enclosed in the Mumetal shield 138 in a manner similar to the head of FIGURE 2. The electron gun structure comprises a filament 139, cathode 140, first grid structure 141, second grid structure 142 and converging anodes 144 and .145. As indicated in FIGURE 16, the anodes 144 and 145 are very thin in conformance with the capillary portion 136 of the envelope.

For defining a magnetic field in the capillary portion of the tube for inter-action with the stream of electrons, a thin washer-like pole piece structure 150 is provided which is secured at 151 to the shield 2138. The shield is, of course, provided with a non-magnetic opening for receiving the pole structure 15G so that the pole structure is magnetically isolated from the shield. As best seen in FIGURE 17, the pole structure 150 comprises a pair of pole pieces 153 and 154 having closely spaced pole portions 155 and 156 for extending on opposite sides of the flattened capillary 136 of the tube, and have more widely spaced portions 157 and 158 terminating in the tape receiving extremities closely spaced to define a pick-up gap 160. As will hereafter be discussed, the pole piece structure 150 is preferably placed at the base of the capillary portion as indicated in FIGURE 15 for best control of the electron stream. As in the embodiment of FIGURE 2, Ithe shield and the pole structure is preferably separate 6 from the tube, so that the tube is removable for replacement.

FIGURES 18, 19 and 20 illustrate a modied pole piece configuration adapted for cooperation with a wide channel recording and comprising pole pieces y165 and 166 having closely spaced pole portions 167 and 168 `for fitting on opposite -sides of the capillary portion of the tube and having wide pole faces such as 169 in FIGURE 20 defining an extended pick-up gap 170. As indicated in FIGURE 18, the pole pieces 165 land 166 may be tapered as at 165a `and have a non-magnetic spacer 171 defining a non-magnetic gap. The head may be provided with windings 172 to allow use of the head as a record or even an erase head. The pole piece configuration of FIGURE 17 could also be provided with such recording windings if desired.

FIGURES 21, 22 and 23 illustrate a -urther modified form of pole piece construction wherein the pole pieces 173 and 174 have closely spaced portions 175 and 176 for fitting over the tube capillary as usual; however the pole pieces have overlapping pole portions 177 and 178 defining an extended gap 179 for `accommodating a relatively wide tape indica-ted diagrammatically at 181.

FIGURES 24 and 25 illustrate a pole mounting structure for the poles of FIGURES 18, 19 and 20 wherein each pole piece such as the pole piece 165 is embedded in a resin material 185 which is cut Iaway as indicated at 186 to accommodate the capillary portion of the tube such yas'the portion 136 in FIGURE 15. It will be unders-tood that a half of the assembly such as shown in FIGURE 24 is placed on each side of the capillary section 136 in FIGURE 15 to provide a pole piece configuraltion similar .to that indicated in FIGURE 18.

FIGURE 26 illustrates a tube comprising an enlarged envelope portion 190, land a capillary portion 191 for receiving a pole piece construction such as 150. The tube has ya filament 192, cathode 193, first grid structure 194, and second grid structure 195. However, in this embodiment, the anodes 196 and 197 `follow a somewhat devious course and include elongated parallel portions 198 and 199 in the capillary section 191. The anodes are of the thin construction such as indicated in FIGURE 16. For protecting the anodes 196 and 197 from stray beam currents, a shield or bafiie element 200 is provided at the potential of the first grid and interposed between the grid structure and the adjacent portions of the anodes.

FIGURE 27 illustrates a suitable circuit for an electron-cloud transducer tube 230 having am envelope 235 with a reduced cross section elongated capillary portion 236 and `a filament 239, cathode 240, first grid 241, second grid 242, and anodes 244 and 245. Typical operating values `for the circuit of FIGURE 27 are as follows: Filament voltage, 9 volts; cathode, zero Volts; yfirst grid, 2.9 volts; second grid, volts, anode 244, 39 volts; anode 245, 41 volts; condensers C1 and C2, 0.1 microfarad; resistors R1 and R2, 600,000 ohms. With these values the anode currents from anodes 244 and 245 were each microamperes. Resistors R1 or R2 or both may be variable to adjust `for balance, although the system works well with `as much as a 2 tol unbalance in anode currents. The system is also not critical with respect to `operating grid and anode voltages; for example, dropping the anode voltage to about 3 volts reduced the anode current Ito 46 microamperes, but still gave good sensitivity (at reduced power handling capacity). Grid voltages can :be changed by a factor of 2 to 1 or more without serious harm. If the filament is operated from an alternating current source hum may be reduced by operating the center tap yof the filament about 25 volts positive with respect to the cathode.

Operation of the `anodes below 100 volts, and preferably below 50 volts is advantageous because secondary .emissioneiectsare reduced, deflection sensitivity yis increased, and the noise level -is lower.

YFor-response to DC., condensers C1 vand'C2 may be omi-tted,'ano=de 245 tapped 'directly at operating potential rand anode-244- directly coupled ,to the D.C. amplifier ciror better stillpushpull direct coupled output from anodes-244 and 245 may be employed. Transverserecor-ding is desirableif extremely long wavelengths .are to xbesensed. It has been'found that great sensitivity can be obtained by thin pole pieces such as 150 illustrated in FIGURE 17, as close to the base-25)` of the capillary l236 as possible. An'irnportant` feature of the invention is-tohave the electron control elements yat a positive potential to attain land directthe electron stream in conjunction with .the magnetic deflection means, and

iSupply voltage Output in db lnallfforms itis important to baiile and isolate the iilag f ment and-cathode emissionV in such away that only the beam coming through the aperture strikes 'the anode electrdes. Hum,v noise, unbalance, and insensitivity will resultvfro'ml unwanted stray emission. VThe heater should benonlinductivelywound, with the yleads and connections closely spaced. A high voltage low current heater should be ..used, -thus allowing suficient wattage -a-t low Vheater current, and reducing fields due to heater current.

It is 'desirableito "cover the glass capillary portion or end ofithevtube with Aquadag and'lampblack, for low secondary emissionand for electrostaticshielding purposes. vThe same effect can be obtained with a conductive electrode properly coated and positioned` "FIGURE 28 'represents a plot of output in db from anode-"244 (taking' zero db at one millivolt) as a function cfr input 'in dbat 1000 cycles.

fFIGURE 29 Ais a-plotof the relative output in (db as a tunctioniof the distance of the pole pieces structure 150 fromlthe base 250 of the capillary portion 236. The plot illustrates the decrease in sensitivity-as the pole piece structurelis movedalong thecapillary portionV 236 away from theflenlarged-envelope portion 235. The plot thus shows theldesirabilityfofhavingI the'pole piece structure 156` as close to thebaseof thecapillary portion-as possible.

f In FIGURESO'is illustrated a frequency response curve of Vrelative output in db asV a function offrequency in cycles perwsecond. The curvelis taken for a 0.014 inch thickMumetal head-similar -to that in FIGURE 27. The fall-off of response at high frequency is due to core loss. Heads of ferritematerial would insure a response to the megacycle range.

.In'FIGURUES "3l, V32 and 33 .is illustrated a at face type .electron-cloud'transducer head having a generally cylindrical envelope 210 with the usual filament 211, cathodef212,'l'irst and second grids 213 and'214, and with generally rectangular anodes 216 and 217 on the flat end face L2180i the tube. The pole piece configuration 219V is disposed against the exterior `face of the end 218, and theelectronstream is induenced bythe rfringing field' bef tween-the pole pieces 221-and`222, which field is sulfi- `cient to cause deflectionof the electron cloud in theitube shown and to produce an output'from vthe tube. As indicatedin'FIGURE 33, the pole structure 219 Iincludesfa non-magnetic ygap 223 for receiving azrecord member thereacross to induce the signal lield across the poles 221 and 222.

FIGURE 34 illustrates an valternative conliguration of the anodes wherein the anodes comprise` half round plates 225 and 226 at the end of the tube 219.

FIGURE 35 illustrates a still further modified form of the electron-cloudtransducer'head of the present invention having a suitable electron beam structure 260 for directing a stream ofl electrons through the constricted neck portion 261 of the envelope 262, the anode portion of the tube 264 having anodes 265 and 266 along opposite sides thereof. A pole piece structure 267 similar to V in FIGURE 17 deflects the electron beamin accordance with a recorded signal as in the previous embodiments.

FIGURE 35 illustrates a short capillary design with the pole pieces 270 and 271 defining `a eld for interaction withthe stream of electrons and having a Vgap 272 for cooperation with a record member traveling thereacross. The envelope 273 is provided with a short capillary portion 274 receiving the pole pieces 270 and271A and has any suitable electron gun structure 275, and anodes such as 276.

In FIGURES 37 and 38 is illustrated aimicrophone Yutilizing anelectron-cloud tube as the transducing element wherein the reference numeral 280 designates a diaphragm of magnetic material to be set in vibration relative to a magnet structure 281 by lmeans of a sound waveA to vary the magnetic eld a agap 282 inthe magnetic circuit of the device. An elongated-capillary.portion283.of the electron-cloud tube 284 extends into the gap 282-for sensing the varying magnetic field and to convert thesame into an electrical signal at the anodes285 and286 asin the previous. embodiments.

Similarly asindicated in FIGURE 39, the electroncloud tube of lthe present invention is suitable for useas a phonograph pick-up, vibration pick-up and the like, the tube 297 .being substituted for the conventional coil, and sensingfany unbalance-between the magnetic field produced by the upper poles 298,299 of the upper magnetic circuit including series aiding permanent magnets 301, 302.and gap @303, and the eld produced by-the lower poles 305, '306 of the lower magnetic circuit including. seriesaidingpermanent magnets 308, 309 and non-magnetic gap 310. These magnetic circuits may be spaced from eachother longitudinally of the beam, so that the "beam is deectediirst one way by one circuit, and then the opposite way by the second circuit. The upper and lower magnetic circuits may ybe initially balanced to produce equal and `opposite magnetic fields with respect to the transducer 297 so that the electron stream will be evenly -distributed Ibetween the anodes 312 -and 313 thereof. The magnetic elds 'may be unbalanced by movement of the magnetic member 315 controlling the reluctance of the gap..310, and it will be understood that theemember 315 may be vibrated by a phonograph needle or other similar vibration pick-up device. In a modified form of this pick-up, pole pieces 293, 299, 305, 306 would be bent or shapedV so that gaps 303 and 310 were on opposite sides of member 31S, thus eliminating any unbalanced' forces on the vibrating element 315. Thus the electron-cloud transducer tube of the present invention can be used wherever a magnetic type pick-up is applicable, by substituting a gap and capillary for the conventional coil.

VIn FIGURE V40 is illustrated a reflection typetransducer head wherein an electron stream indicated at -320 is directed into a capillary portion 321 of a tube 322 by means'of-anfelectron gun structure 323, and is reflected from the capillary portion by means of a surface325-at the end'of` the capillary at cathode potential or 4slightly negative with respect to the cathode. The surface 325 may be provided by an Aquadag coating on the capillary wall, or the capillary wall itself may be maintained at cathode potential under suitable conditions. The capillary section 321 thus constitutes a low velocity region, the electrons traveling from this region in the reverse direction to the anodes 327 and 32S along paths such as indicated at 329.

As indicated in FIGURE 40 and 4l, a magnetic field may be applied to the capillary section 321 to deect the returning electron beam 329 by means of a magnetic pole structure indicated at 331, the pole structure comprising a pair of poles 332 and 333 on opposite sides of the capillary portion 321 and having a non-magnetic gap 335 for receiving a record member 336 thereacross in the direction of the arrow 337 in FIGURE 4l. As in the previous embodiments, the presence of a magnetic field between the poles 332 and 333 causes electron flow to one of the anodes 327 or 328 to predominate to produce an electric potential between the anodes. The electron gun construction and the circuit connections previously described, such as in FIGURES ll, l2 and 27 are directly applicable to the modified tubes of FIGURES 4() and 4l, with the addition, if necessary of a grounding or biasing connection to surface 325. A magnetic shield 34) is indicated which may be similar to the shield shown in FIGURE 2. It will be appreciated that the pole structure 331 serves to shield the capillary portion of the tube from stray magnetic iields.

It will be understood that the path of the reiiected beam indicated diagrammatically in FIGURE 40 is merely for illustration and that diierent paths will be followed depending on operating conditions and magnetic pole conguration.

Instead of the anodes 327 and 32S, the input of an electron multiplier can be substituted and the transducer output taken from the output of the multiplier. This eliminates Johnson noise and other effects that would result from ordinary amplilication of the anode output. If the multiplier input is partially shaded from the net return beam, a single multiplier section will respond to variations in positon of the return beam.

FIGURES 42 and 43 indicate a transducer tube substantially identical to that shown in FIGURES 40 and 4l and the same reference numerals have been applied to corresponding parts. However, in this case a pole structure 350 is utilized having a relatively broad gap 351, FIGURE 43, disposed radially outwardly of the tube rather than at the end face thereof as in FIGURE 4l. The pole structure has relatively wide pole faces 352 and 353 for deiining a magnetic iield for inuencing the reflected stream of electrons 356, and in FIGURE 42, it is assumed that a magnetic field exists between the poles 352 and 353 so that ow of reected electrons is predominately to the anode 328. Here again the diagrammatically illustrated electron ow path is merely by way of illustration.

In FIGURE 44 is illustrated a further form of a reiiected type transducer head wherein an envelope 360 has a capillary portion 361 with a stream of electrons 362 directed by an electron gun structure 363 against a target 365 which is a good secondary emitter. The operation is similar to the embodiment of FIGURE 40, and a similar pole structure may be used for deecting the secondary stream of electrons 367 for example to anode 370 as indicated.

Those skilled in the art will appreciate that electric circuits such as illustrated in FIGURES ll and 12 may be utilized to sense electron flow variation at the anodes of any of the illustrated embodiments.

It will be understood that modications and variations may be effected Without departing from the Scope of the novel concepts of the present invention.

I claim as my invention:

l. An electromagnetic transducer device comprising an envelope, magnetic pole means delining a magnetic lield extending into a region of said envelope, means for directing a stream of electrons into said region, a surface in said region at a potential to reject Said stream of electrons, an electrode spaced from said surface and at a p0- tential to attract said electrons in a generally reverse direction, and means for sensing the etect of said magnetic iield on said reverse ow of electrons.

2. A magnetic transducer device comprising an envelope, means for establishing a stream of electrons within said envelope, means entirely external of said envelope disposed to establish a magnetic field for interaction with said stream of electrons, means for varying said magnetic iield in accordance with an intelligence signal, means for obtaining an electric output Varying in accordance with said eld, and means lwhereby said stream of electrons has a reversal of direction of movement in the region of interaction with said magnetic field.

3. In combination, a magnetic record medium having a signal recorded thereon and a device `for electrically reproducing the signal recorded on said record medium comprising an envelope, means for producing a stream of electrical charges in said envelope, said envelope having a constricted portion providing an external wall surface in close proximity to said stream of electrical charges, means defining a magnetic iiux path for the magnetic signal linx of the record medium extending from the record medium through said external wall surface and into the path of said stream of electrical charges in said envelope, and means for retarding the velocity of said stream of electrical charges in the region of intersection thereof with said magnetic flux path.

4. In combination, a magnetic record medium having a signal recorded thereon and a device for electrically reproducing the signal recorded on said record medium comprising an envelope, means for producing a stream of electrical charges in said envelope, said envelope having a constricted portion providing an external wall surface in close proximity to said stream of electrical charges, means defining a magnetic -ux path for the magnetic signal flux of the record medium extending from the record medium through said external wall surface and into the path of said stream of electrical charges in said envelope, and means for retarding the velocity of said stream of electrical charges in the region of intersection thereof with said magnetic flux path, said retarding means comprising a lcontrol surface Within said envelope toward which said stream of electrical charges is directed and which is maintained at a potential to repel said stream of electrical charges to cause a reversal in the direction of movement of said stream of electrical charges near Where said magnetic liux path intersects said stream.

5. In combination, a magnetic record medium having a signal recorded thereon and a device for electrically reproducing the signal recorded on said record medium comprising an envelope, means for producing a stream of electrical charges in said envelope, said envelope having a constricted portion providing an external wall surface in close proximity to said stream of electrical charges, means defining a magnetic ilux path for the magnetic signal ilux of the record medium extending from the record medium through said external wall surface and into the path of said stream of electrical charges in said envelope, and means for retarding the velocity of said stream of electrical charges in the region of intersection thereof with said magnetic flux path, said stream producing means comprising a cathode for emitting a stream of electrons and focusing and accelerating means for directing said stream along a path adjacent said external wall surface, and said retarding means comprising a control surface within said envelope toward which said stream of electrons is directed and which is maintained in the neighborhood of cathode potential.

6. A magnetic transducer device comprising an envelopethavingsanend portion With-at Yexterior side wall surfaces which are very closely spaced in comparison JWith other=externa1 dimensions of said envelope, means for-directinga stream of electrical charges into said end portion of said envelope, and means deiiningA a magnetic ux path for a magnetic signal flux extending-*through 'said-flat exteriorside Wall-surfaces-of said envelope and intersecting thepath of said stream of electrical charges, and'means for reversing-the direction of movement of said'stream'of electrical charges in said end portion of said envelope,

'7. AAmagnetic transducer device comprising an envelope, means'for-producing va stream of electrical charges insaid envelope, means for coupling to a magnetic record medium defining a lmagnetic lux path for a magnetic signalilux from-the record medium intersecting a region vof the path of said stream of electrical charges, and means for retardin-g the lmagnitude of the velocity of said stream ofV electrical charges in said region of thepath thereof.

Av8. A magnetic transducer device comprising an envelope,-meansforproducing a stream of electrical charges insaidenvelope, means deiining a magnetic -ilux path for ya magne'tiosignaliiux intersecting a region of the path of said'stream of electrical charges, and means for retarding 'the velocity ofsaid stream at said region of the path thereoffsaidretarding meanscomprising a control surface in saidenvelope toward which said stream is directed Yand Whi'chiis-maintained at a potential to repel said electrical charges.

*9. A magnetic transducer device comprisingan envelope, Vmeans tor-producing a stream of electrical charges in said envelope, means for coupling to a magnetic record medium and deiininga magnetic flux path for -a magnetic'y signal ux fromthe record medium intersecting la region of the path 'ofsaid` stream of electrical fcharges, means for reversing the direction-of movement of `said stream of electrical charges near said-region'oftthepath o''saidvstrearm and means forelectr-ically sensing Vthe ifect of said signal-fluxfrom the recordmedium' on said stream 'ofelectrical charges. A10. 'A- magnetic transducer devicecomprising'anenvelopefmeans for producinga stream of `electrical charges inrsaid envelope, meansdefining a'magneticiiuxrpath for a magnetic lsignal linx intersecting va region'of thepath frsaid stream of' electrical charges,V and means for retarding'the-magnitude of the velocityi'of'saidstreamat said region ofY the path thereof, said streamproducing'means comprising la cathodeV for emitting a stream of'electrons and focusing and Vaccelerating means `for directing'said 'streamalong itspath Within said envelope, and said retarding meansv comprising a control surface adj acent said region of 'saidpath and Vwhich is'maintainedinrthe neighborhood of cathode potential.

Z1'1. 'Amagnetic playback 'head kfor electrically reproducing a-magnetic signal comprising Van envelope,a surface in said envelope, means for directinga streamof `electrical charges toward said surface `comprising -accelerat- 'ing means having an accelerating voltage4 of' aY value to accelerate -said velectrical charges ktoward V-said Vvsurface, means for applying a retarding voltage to 'said surface whichis-iless thansaid accelerating voltage,` means'whereby .said surface is operative tofret'ardzthe accelerationof said .electrical :charges to lcreate a cloud .of electrical chargesrin a region of saidcenvelope when said retarding voltage is applied to sai'dzsurface, means forapplying a magnetic signal lield tosaid cloud of electrical charges directlyat saidregion, andmeans for electrically sensing the 'effect of said magnetic `signaltield on said electrical charges.

'12. A magnetic playback heat for electrically reproducing a magnetic signalfcomprising an envelope, a surface in said envelope, lmeanstor directing astrearnof electrical charges:towardsaid'surface comprising accelerating means having an accelerating voltage of a value to accelerate said electrical charges `toward said surface, means fora-pplying a retard-ing-voltage to said surface which is lesstnan said accelerating voltage, means ywhere- Ioysaid surface is operative Vto retard the acceleration of ysaid electricalcharges to create a cloud of electrical charges in a regionA of said envelope when said retarding voltage is applied to Isa-id surface, means for applying la magnetic `signal iield to said ,cloud of electricaicharges directly at saidiregion, and means for electrically sensing' the Veiect of said magnetic signalziield on said electrical charges, said magnet-icsignalrfield applying means comprising a magnetic coreentirelyy external ofsaid envelope dening -a'magnetic flux path having its shortest length Awithin said envelope extending directly through said region and being entirely in-,space Withinsaid envelope, and the interior of said envelope being entirely free of magnetic i, material in V'sai-d region.

15. VA1magnetic playbacltihead -or electrically-reproducing a magneticzsign'alcomprising an envelope, a surface in said-envelope,:rnea`nstorr directing a stream of electrical charges toward said surface comprising accelerating means havingan accelerating'voltage of a value to .accelerate said Aelectrical Vchargestoward said surface, means for applying a retarding voltage to said surface which is less than said accelerating voltage,'means wherelby said surface with said retarding voltage `applied thereto is:operative to create a cloud ofelectrical charges having Ya ,substantially minimum velocity amplitude yin a region of said envelope remote fromsaid accelerating means, means forapplying .a magnetic .signal iield to said cloud of electricalrcharges with the maximum of Vthe lsignal field in the 'envelope directlyintersecting said region Where said electrical .charges have substantiaily their minimum velocity, rand means forelectrically sensing the effect of said magneticsignal field onsaid electrical charges.

.References-Cited in the tle of this patent UNITED STATES'PATENTS 

